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Chapter 19: The Cardiovascular System – Blood Vessels
Objectives
Part 1: Blood Vessel Structure and Function
Structure of Blood Vessel Walls
1. Describe the three layers that typically form the wall of a blood vessel, and state the function of each.
2. Define vasoconstriction and vasodilation.
Arterial System
3. Compare and contrast the structure and function of the three types of arteries.
Capillaries
4. Describe the structure and function of a capillary bed.
Venous System
5. Describe the structure and function of veins, and explain how veins differ from arteries.
Part 2: Physiology of Circulation
Introduction to Blood Flow, Blood Pressure, and Resistance
6. Define blood flow, blood pressure, and resistance, and explain the relationships between these factors.
Systemic Blood Pressure
7. Describe how blood pressure differs in the arteries, capillaries, and veins.
Maintaining Blood Pressure
8. List and explain the factors that influence blood pressure, and describe how blood pressure is regulated.
9. Define hypertension. Describe its manifestations and consequences.
Blood Flow Through Body Tissues: Tissue Perfusion
10. Explain how blood flow is regulated in the body in general and in specific organs.
11. Outline factors involved in capillary dynamics, and explain the significance of each.
12. Define circulatory shock. List several possible causes.
Part 3: Circulatory Pathways: Blood Vessels of the Body
The Two Main Circulations of the Body
13. Trace the pathway of blood through the pulmonary circuit, and state the importance of this special circulation.
14. Describe the general functions of the systemic circuit.
Principal Vessels of the Systemic Circulation
15. Name and give the location of the major arteries and veins in the systemic circulation.
16. Describe the structure and special function of the hepatic portal system.
Developmental Aspects of Blood Vessels
17. Explain how blood vessels develop.
18. Provide examples of changes that often occur in blood vessels as a person ages.
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Suggested Lecture Outline
Part 1: Blood Vessel Structure and Function (pp. 693–701; Figs. 19.1–19.5; Table 19.1)
I. Structure of Blood Vessel Walls (p. 693; Figs. 19.1–19.2; Table 19.1)
A. The walls of all blood vessels except the smallest consist of three layers: the tunica intima, tunica media, and
tunica externa (p. 693; Fig. 19.1).
B. The tunica intima reduces friction between the vessel walls and blood; the tunica media controls vasoconstriction
and vasodilation of the vessel; and the tunica externa protects, reinforces, and anchors the vessel to surrounding
structures (p. 693; Fig. 19.2; Table 19.1).
II. Arterial System (pp. 693–696; Fig. 19.2; Tables 19.1–19.2)
A. Elastic, or conducting, arteries contain large amounts of elastin, which enables these vessels to withstand and
smooth out pressure fluctuations due to heart action (pp. 693–695; Fig. 19.2; Table 19.1).
B. Muscular, or distributing, arteries deliver blood to specific body organs and have the greatest proportion of tunica media of all vessels, making them more active in vasoconstriction (p. 696; Table 19.1).
C. Arterioles are the smallest arteries and regulate blood flow into capillary beds through vasoconstriction and
vasodilation (p. 696).
III. Capillaries (pp. 696–698; Figs. 19.3–19.4; Table 19.1)
A. Capillaries are the smallest vessels and allow for exchange of substances between the blood and interstitial fluid (pp. 696–698; Fig. 19.3; Table 19.1).
1. Continuous capillaries are most common and allow passage of fluids and small solutes.
2. Fenestrated capillaries are more permeable to fluids and solutes than continuous capillaries.
3. Sinusoid capillaries are leaky capillaries that allow large molecules to pass between the blood and surrounding tissues.
B. Capillary beds are microcirculatory networks consisting of a vascular shunt and true capillaries, which function
as the exchange vessels (p. 698; Fig. 19.4).
C. A cuff of smooth muscle, called a precapillary sphincter, surrounds each capillary at the metarteriole and acts as a
valve to regulate blood flow into the capillary (p. 698; Fig. 19.4).
IV. Venous System (pp. 698–699; Fig. 19.5; Table 19.1)
A. Venules are formed where capillaries converge and allow fluid and white blood cells to move easily between
the blood and tissues (p. 698; Table 19.1).
B. Venules join to form veins, which are relatively thin-walled vessels with large lumens containing about 65% of
the total blood volume (pp. 698–699; Fig. 19.5; Table 19.1).
V. Vascular Anastomoses (pp. 699–701)
A. Vascular anastomoses form where vascular channels unite, allowing blood to be supplied to and drained from
an area even if one channel is blocked (p. 699).
Part 2: Physiology of Circulation (pp. 701–720; Figs. 19.6–19.18;
Table 19.2)
VI. Introduction to Blood Flow, Blood Pressure, and Resistance (pp. 701–702)
A. Blood flow is the volume of blood flowing through a vessel, organ, or the entire circulation in a given period
and may be expressed as ml/min (p. 701).
B. Blood pressure is the force per unit area exerted by the blood against a vessel wall and is expressed in millimeters of mercury (mm Hg) (pp. 701–702).
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C. Resistance is a measure of the friction between blood and the vessel wall and arises from three sources: blood
viscosity, blood vessel length, and blood vessel diameter (p. 702).
D. Relationship Between Flow, Pressure, and Resistance (p. 702)
1. If blood pressure increases, blood flow increases; if peripheral resistance increases, blood flow decreases.
2. Peripheral resistance is the most important factor influencing local blood flow, because vasoconstriction or
vasodilation can dramatically alter local blood flow, while systemic blood pressure remains unchanged.
VII. Systemic Blood Pressure (pp. 702–704; Figs. 19.6–19.7)
A. The pumping action of the heart generates blood flow; pressure results when blood flow is opposed by resistance (p. 702).
B. Systemic blood pressure is highest in the aorta and declines throughout the pathway until it reaches 0 mm Hg
in the right atrium (pp. 702–703; Fig. 19.6).
C. Arterial blood pressure reflects how much the arteries close to the heart can be stretched (compliance, or distensibility) and the volume forced into them at a given time (p. 703; Fig. 19.6).
1. When the left ventricle contracts, blood is forced into the aorta, producing a peak in pressure called systolic
pressure (120 mm Hg).
2. Diastolic pressure occurs when blood is prevented from flowing back into the ventricles by the closed semilunar valve and the aorta recoils (70–80 mm Hg).
3. The difference between diastolic and systolic pressure is called the pulse pressure.
4. The mean arterial pressure (MAP) represents the pressure that propels blood to the tissues.
D. Capillary blood pressure is low, ranging from 15–40 mm Hg, which protects the capillaries from rupture but is
still adequate to ensure exchange between blood and tissues (p. 703; Fig. 19.6).
E. Venous blood pressure changes very little during the cardiac cycle and is low, reflecting cumulative effects of
peripheral resistance (pp. 703–704; Fig. 19.7).
VIII. Maintaining Blood Pressure (pp. 704–711; Figs. 19.8–19.12; Table 19.2)
A. Blood pressure varies directly with changes in blood volume and cardiac output, which are determined primarily by venous return and neural and hormonal controls (p. 704; Fig. 19.8).
B. Short-term neural controls of peripheral resistance alter blood distribution to meet specific tissue demands
and maintain adequate MAP by altering blood vessel diameter (pp. 704–707; Fig. 19.9).
1. Clusters of neurons in the medulla oblongata, the cardioacceleratory, cardioinhibitory, and vasomotor centers, form the cardiovascular center that regulates blood pressure by altering cardiac output and blood vessel diameter.
2. Baroreceptors detect stretch and send impulses to the vasomotor center, inhibiting its activity and promoting vasodilation of arterioles and veins.
3. Chemoreceptors detect a rise in carbon dioxide levels of the blood and stimulate the cardioacceleratory and
vasomotor centers, which increases cardiac output and vasoconstriction.
4. The cortex and hypothalamus can modify arterial pressure by signaling the medullary centers.
C. Chemical controls influence blood pressure by acting on vascular smooth muscle or the vasomotor center (p.
707; Table 19.2).
1. Norepinephrine and epinephrine promote an increase in cardiac output and generalized vasoconstriction.
2. Atrial natriuretic peptide acts as a vasodilator and an antagonist to aldosterone, resulting in a drop in blood
volume.
3. Antidiuretic hormone promotes vasoconstriction and water conservation by the kidneys, resulting in an increase in blood volume.
4. Angiotensin II acts as a vasoconstrictor, as well as promoting the release of aldoste-rone and antidiuretic
hormone.
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5. Endothelium-derived factors promote vasoconstriction and are released in response to low blood flow.
6. Nitric oxide is produced in response to high blood flow or other signaling molecules and promotes systemic
and localized vasodilation.
7. Inflammatory chemicals, such as histamine, prostacyclin, and kinins, are potent vasodilators.
8. Alcohol inhibits antidiuretic hormone release and the vasomotor center, resulting in vasodilation.
D. Long-Term Regulation: Renal Mechanisms (pp. 708–710; Figs. 19.10–19.11)
1. The direct renal mechanism counteracts an increase in blood pressure by altering blood volume, which increases the rate of kidney filtration.
2. The indirect renal mechanism is the renin-angiotensin-aldosterone mechanism, which counteracts a decline
in arterial blood pressure by causing systemic vasoconstriction.
E. Monitoring circulatory efficiency is accomplished by measuring pulse and blood pressure; these values together with respiratory rate and body temperature are called vital signs (p. 710; Fig. 19.12).
1. A pulse is generated by the alternating stretch and recoil of elastic arteries during each cardiac cycle.
2. Systemic blood pressure is measured indirectly using the auscultatory method, which relies on the use of a
blood pressure cuff to alternately stop and reopen blood flow into the brachial artery of the arm.
F. Alterations in blood pressure may result in hypotension (low blood pressure) or transient or persistent hypertension (high blood pressure) (pp. 710–711).
IX. Blood Flow Through Body Tissues: Tissue Perfusion (pp. 711–720;
Figs. 19.13–19.18)
A. Tissue perfusion is involved in delivery of oxygen and nutrients to, and removal of wastes from, tissue cells; gas
exchange in the lungs; absorption of nutrients from the digestive tract; and urine formation in the kidneys (pp.
711–712; Fig. 19.13).
B. Velocity or speed of blood flow changes as it passes through the systemic circulation; it is fastest in the aorta
and declines in velocity as vessel diameter decreases (p. 712; Fig. 19.14).
C. Autoregulation: Local Regulation of Blood Flow (pp. 712–713; Fig. 19.15)
1. Autoregulation is the automatic adjustment of blood flow to each tissue in proportion to its needs and is controlled intrinsically by modifying the diameter of local arterioles.
2. Metabolic controls of autoregulation are most strongly stimulated by a shortage of oxygen at the tissues.
3. Myogenic control involves the localized response of vascular smooth muscle to passive stretch.
4. Long-term autoregulation develops over weeks or months and involves an increase in the size of existing
blood vessels and an increase in the number of vessels in a specific area, a process called angiogenesis.
D. Blood Flow in Special Areas (pp. 713–716)
1. Blood flow to skeletal muscles varies with level of activity and fiber type.
2. Muscular autoregulation occurs almost entirely in response to decreased oxygen concentrations.
3. Cerebral blood flow is tightly regulated to meet neuronal needs, because neurons cannot tolerate periods of
ischemia, and increased blood carbon dioxide causes marked vasodilation.
4. In the skin, local autoregulatory events control oxygen and nutrient delivery to the cells, while neural mechanisms control the body temperature regulation function.
5. Autoregulatory controls of blood flow to the lungs are the opposite of what happens in most tissues: low
pulmonary oxygen causes vasoconstriction, while higher oxygen causes vasodilation.
6. Movement of blood through the coronary circulation of the heart is influenced by aortic pressure and the
pumping of the ventricles.
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E. Blood Flow Through Capillaries and Capillary Dynamics (pp. 716–717; Figs. 19.16–19.17)
1. Vasomotion, the slow, intermittent flow of blood through the capillaries, reflects the action of the precapillary sphincters in response to local autoregulatory controls.
2. Capillary exchange of nutrients, gases, and metabolic wastes occurs between the blood and interstitial
space through diffusion.
3. Hydrostatic pressure (HP) is the force of a fluid against a membrane.
4. Colloid osmotic pressure (OP), the force opposing hydrostatic pressure, is created by the presence of large,
nondiffusible molecules that are prevented from moving through the capillary membrane.
5. Fluids will leave the capillaries if net HP exceeds net OP, but fluids will enter the capillaries if net OP exceeds
net HP.
F. Circulatory shock is any condition in which blood volume is inadequate and cannot circulate normally, resulting
in blood flow that cannot meet the needs of a tissue (p. 717; Fig. 19.18).
1. Hypovolemic shock results from a large-scale loss of blood, and may be characterized by an elevated heart
rate and intense vasoconstriction.
2. Vascular shock is characterized by a normal blood volume accompanied by extreme vasodilation, resulting
in poor circulation and a rapid drop in blood pressure.
3. Transient vascular shock is due to prolonged exposure to heat, such as while sunbathing, resulting in vasodilation of cutaneous blood vessels.
4. Cardiogenic shock occurs when the heart is too inefficient to sustain normal blood flow and is usually related
to myocardial damage, such as repeated myocardial infarcts.
Part 3: Circulatory Pathways: Blood Vessels of the Body (pp. 721–745; Figs. 19.19–19.30; Tables 19.3–19.13)
X. The Two Main Circulations of the Body (p. 721; Figs. 19.19–19.20; Table 19.3)
A. Two distinct pathways travel to and from the heart: pulmonary circulation runs from the heart to the lungs and
back to the heart; systemic circulation runs to all parts of the body before returning to the heart.
XI. Systemic Arteries and Veins: Differences in Pathways and Courses (p. 721;
Fig. 19.29; Table 19.12)
A. There are some important differences between arteries and veins (p. 721; Table 19.12).
1. There is one terminal systemic artery, the aorta, but two terminal systemic veins: the superior and inferior
vena cava.
2. Arteries run deep and are well protected, but veins are both deep, which run parallel to the arteries, and
superficial, which run just beneath the skin.
3. Arterial pathways tend to be clear, but there are often many interconnections in venous pathways, making
them difficult to follow.
4. There are at least two areas where venous drainage does not parallel the arterial supply: the dural sinuses
draining the brain, and the hepatic portal system draining from the digestive organs to the liver before entering the main systemic circulation (Fig. 19.29).
XII. Principal Vessels of the Systemic Circulation (pp. 721–745; Figs. 19.19–19.30; Tables 19.3–19.13)
In the following sections (XII. A.–K.), vessels have been arranged in tables in order to facilitate presentation by the
instructor. More commonly taught vessels are presented, as well as the branching pattern of these vessels, indicated as “levels.” Also, general areas served by the listed vessels are presented.
A. The pulmonary circulation functions only to bring blood into close contact with the alveoli of the lungs for gas
exchange and then circulates it back to the heart to be pumped out to the rest of the body (pp. 722–723; Fig.
19.19; Table 19.3).
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Pulmonary Circulation
Start
Level 1
Level 2
Level 3
R. ventricle
of heart
Level 4
Level 5
End
Main vessel
out of R.
ventricle 
Vessels
arising
from
Level 1 
Vessels
arising
from
Level 2 
Vessels
arising from
Level 3 
Vessels
arising from
Level 4 
L. atrium
of heart
Pulmonary
trunk
R. and L.
pulmonary
arteries
Lobar
arteries
Pulmonary
capillaries
Pulmonary
veins
B. The aorta is the largest artery in the body and has discretely named regions that extend from the heart to the
lower abdominal cavity (pp. 724–725; Fig. 19.21; Table 19.4).
Systemic Circulation: Aorta and Major Arteries
Level 1
Main
Vessel
Aorta
Divisions of
Aorta
Level 2
Level 3
Ascending aorta
R. and
L. coronary
arteries
Aortic arch
Brachiocephalic
artery
Myocardium of heart
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L. common
carotid
L. side of head and neck
L. subclavian
artery
L. upper limb
R. common carotid
R. side of head and neck
R. subclavian
artery
R. upper limb
Thoracic aorta
Abdominal
aorta
Area Served by
Vessel
Thorax wall and viscera
R. and L.
common iliac
arteries
CHAPTER 19
R. and L. lower limb, pelvic cavity
The Cardiovascular System: Blood Vessels
235
C. The common carotid arteries supply blood to the head and neck (pp. 726–727; Fig. 19.22; Table 19.5).
Systemic Circulation: Arteries of the Head and Neck
Level 1
Main
Vessel
Level 2
Level 3
Common
carotid
arteries
(R. and L.)
External
carotid
arteries
Superficial
temporal
arteries
Parotid gland and
scalp
Facial
arteries
Skin and muscles
of face
Anterior
cerebral
arteries
Frontal and
parietal lobes of
brain
Middle
cerebral
arteries
Temporal,
parietal, and
frontal lobes of
the brain
Internal
carotid
arteries
Subclavian
arteries
(R. and L.)
236
Vertebral arteries
Basilar
artery
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Level 4
Level 5
Posterior
cerebral
arteries
Area Served by
Vessel
Occipital and
temporal lobes of
the brain
Anterior
communicating
artery
Arterial
anastomosis
connecting R. and
L. anterior
cerebral arteries
(Circle of Willis)
Posterior
communicating
arteries
Arterial
anastomoses
connecting
posterior cerebral
arteries to middle
cerebral arteries.
(Circle of Willis)
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D. The subclavian arteries supply blood to the upper limbs (pp. 728–729; Fig. 19.23; Table 19.6).
Systemic Circulation: Arteries of the Upper Limbs
Level 1
Main
Vessel
Level 2
Level 3
Level 4
Level 5
Level 6
Subclavian
arteries
(R. and L.)
Axillary
arteries
Brachial
arteries
Radial
arteries
Deep
palmar
arches
Metacarpal
arteries
Ulnar
arteries
Superficial
palmar
arches
Digital
arteries
Area Served
by Vessel
Arm,
forearm,
hand, fingers
E. The arteries supplying the abdomen arise from the abdominal aorta (pp. 730–733;
Fig. 19.24; Table 19.7).
Systemic Circulation: Arteries of the Abdomen
Level 1
Main
Vessel
Abdominal
aorta
Level 2
Level 3
Level 4
Celiac trunk
Common
hepatic
artery
Hepatic artery
Splenic artery
R. gastric
artery
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Level 5
Area Served
by Vessel
Liver
Left gastric
artery
Stomach,
spleen,
pancreas
Stomach
Superior
mesenteric
artery
Small
intestine,
most of large
intestine
Suprarenal
arteries
Adrenal
glands
Renal
arteries
Kidneys
Gonadal
arteries
Ovaries/testes
Inferior
mesenteric
artery
Distal large
intestine
Common
iliac Arteries
Lower limbs,
pelvic cavity
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F. The arterial blood supply to the pelvis and lower limbs is provided by the common iliac arteries, which branch
from the distal end of the abdominal aorta (pp. 734–735; Fig. 19.25; Table 19.8).
Systemic Circulation: Arteries of the Pelvis and Lower Limbs
Level 1
Main
Vessel
Common
iliac
arteries
(R. and L.)
Level 2
Level 3
Level 4
Level 5
Level 6
Internal
iliac
arteries
External
iliac
arteries
Area
Served by
Vessel
Pelvic wall,
viscera, gluteal
muscles
Femoral
arteries
Popliteal
arteries
Anterior
tibial
arteries
Dorsalis
pedis
arteries
Ankle and
foot
Posterior Fibular
Lateral leg
tibial
(peroneal) muscles
arteries
arteries
G. The vena cavae are the major veins that drain blood from the body back toward the heart (pp. 736–737; Fig.
19.26; Table 19.9).
Systemic Circulation: The Vena Cavae and the Major Veins
Area Drained
by Vessel
Level 3
Head and neck
Internal jugular veins
Upper limbs
Subclavian veins
Lower limbs
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Level 2
Level 1 Main Vessel
R. and L.
brachiocephalic
veins
Superior vena cava
Common iliac
veins
Inferior vena cava
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H. Most of the blood drained from the head and neck is collected by three pairs of veins: the external jugular veins, the
internal jugular veins, and the vertebral veins (pp. 738–739; Fig. 19.27; Table 19.10).
Systemic Circulation: Veins of the Head and Neck
Area
Drained by
Vessel
Brain
Level 6
Level 5
Level 4
Level 3
Superior
sagittal
sinus
Straight
sinus
Transverse
sinuses
Level 2
Sigmoid
sinus
Internal
jugular
veins
Level 1 Main
Vessel
Brachiocephalic veins
Inferior
sagittal
sinus
Deep face
and neck
Superficial
temporal
veins
Facial veins
Superficial
face and
neck
External
jugular veins
Subclavian
veins
Vertebral
veins
I. The deep veins of the upper limbs follow the same paths as the arteries of the same name; the superficial veins are
larger than the deep veins and easily seen beneath the skin (pp. 740–741; Fig. 19.28; Table 19.11).
Systemic Circulation: Veins of the Upper Limbs and Thorax
Area
Drained by
Vessel
Level 7
Superficial
forearm
Deep
upper limb
Deep and
superficial
palmar
arches
Level 6
Level 5
Median
cubital
vein
Cephalic
veins
Radial
veins
Brachial
veins
Axillary
veins
Level 3
Level 2
Level 1
Main
Vessel
Subclavian
veins
Brachiocephalic
veins
Superior
vena
cava
R. intercostal veins
Azygos
vein
Basilic
veins
Ulnar
veins
Thoracic
cavity and
chest wall
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Level 4
L. intercostal
veins
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Hemiazygos
vein
The Cardiovascular System: Blood Vessels
239
J. The inferior vena cava returns blood from the abdominopelvic viscera and abdominal walls to the heart (pp. 742–
743; Fig. 19.29; Table 19.12).
Systemic Circulation: Veins of the Abdomen
Area
Drained by
Vessel
Level 6
Level 5
Small intestine, first
half of large
intestine
Superior
mesenteric
vein
Spleen,
stomach,
pancreas
Lower half
of large
intestine
Level 4
Level 3
Hepatic
portal
vein
Level 2
Hepatic veins
Level 1
Main
Vessel
Inferior
vena cava
Splenic
vein
Inferior
mesenteric
vein
Adrenal
glands
Suprarenal
veins
Kidneys
Renal veins
Ovaries,
testes
L. gonadal
vein
R. gonadal vein
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K. Most veins of the lower limbs have the same name as the arteries they accompany (p. 744; Fig. 19.30; Table 19.13).
Systemic Circulation: Veins of the Pelvis and Lower Limbs
Area
Drained
by
Vessel
Level 7
Level 6
Level 5
Level 4
Level 3
Pelvic cavity
organs
and wall
Posterior
tibial
veins
Dorsalis
pedis
veins
Popliteal
veins
Femoral
veins
Level 2
Level
1 Main
Vessel
Internal
iliac veins
Common
iliac veins
External
iliac veins
Anterior
tibial
veins
Fibular
veins
Great
saphenous
veins
XIII.
Developmental Aspects of Blood Vessels (p. 745)
A. The vascular endothelium is formed by mesodermal cells that collect throughout the embryo in blood islands,
which give rise to extensions that form rudimentary vascular tubes.
B. By the fourth week of development, the rudimentary heart and vessels are circulating blood.
C. Fetal vascular modifications include shunts to bypass fetal lungs (the foramen ovale and ductus arteriosus), the
ductus venosus that bypasses the liver, and the umbilical arteries and veins, which carry blood to and from the
placenta.
D. At birth, the fetal shunts and bypasses close and become occluded.
E. Congenital vascular problems are rare, but the incidence of vascular disease increases with age, leading to varicose veins, tingling in fingers and toes, and muscle cramping.
F. Atherosclerosis begins in youth, but rarely causes problems until old age.
G. Blood pressure changes with age: the arterial pressure of infants is about 90/55, but rises steadily during childhood to an average of 120/80, and finally increases to 150/90 in old age.
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